Electrolyte additive for controlling morphology and optics of reversible metal films

ABSTRACT

Dynamic windows with adjustable tint give users greater control over flow of light and heat. Reversible metal electrodeposition dynamic windows include (i) a transparent or translucent conductive electrode; (ii) an electrolyte solution in contact with the electrode, the electrolyte solution comprising metal cations that are reversibly electrodeposited onto the transparent electrode upon application of a cathodic potential; and (iii) a counter electrode. The electrolyte solution advantageously includes a small amount of an additive (e.g., an inhibitor, an accelerator, a leveler, or an organic or inorganic molecule that similarly serves to enhance the surface morphology of the metal cations during reversible metal electrodeposition onto the transparent electrode). Such enhancement of surface morphology during the reversible electrodeposition of the metal tinting layer over the electrode enhances one or more of color neutrality, transmittance characteristics of visible wavelengths (e.g., ability to achieve a near 0% transmission privacy state), infrared reflectance, or switching speed.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority to and the benefit of U.S.Provisional Patent Application No. 63/104,975 filed Oct. 23, 2020,entitled “ELECTROLYTE ADDITIVE FOR CONTROLLING MORPHOLOGY AND OPTICS OFREVERSIBLE METAL FILMS,” which application is herein incorporated byreference in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with government support under grant numberDE-EE0008226 awarded by the U.S. Department of Energy. The governmenthas certain rights in the invention.

BACKGROUND

Dynamic windows control both the light and heat flow in and out ofbuildings while maintaining the view through the glass, thus offeringboth energetic and aesthetic advantages over static controls such asblinds or shades. A recent study by View, Inc. and Cornell Universityshowed that implementing dynamic windows in office buildings can improveemployee productivity by up to 2% through reduced glare and optimaltemperature and lighting control. In addition to the aestheticadvantages, dynamic windows can lead to an average of ˜10-20% energysavings over static low-E windows by decreasing energy consumptionassociated with heating, ventilation, and air conditioning (HVAC).

Over the past several decades, the majority of dynamic window researchhas focused on electrochromic conductive organic molecules andion-intercalation based metal oxide electrochromic materials(particularly WO₃ and NiO_(x)) that change color upon application of avoltage. Despite the numerous promising advantages of such windows overstatic lighting controls, they have yet to achieve widespreadcommercialization due to their inability to simultaneously providelong-term reliability and durability, color-neutral operationalcharacteristics, fast switching on a large-scale, and reasonable cost.

An exciting alternative to electrochromism is reversible metalelectrodeposition (RME). These windows operate through the reversibleelectrochemical deposition of metal on and off a transparent conductingoxide (TCO) electrode, such as indium tin oxide (ITO), fluorine dopedtin oxide (FTO), carbon nanotube, etc. Such windows include anelectrolyte between the electrodes, with solubilized, nearly colorlessmetal cations that can be reduced upon application of a cathodicpotential to the TCO to induce optical tinting. While “transparent” istypically used herein for simplicity in describing the electrode, itwill be appreciated that the scope includes translucent materials aswell.

Reversing the polarity oxidizes the metallic film, effectively strippingit back into the electrolyte, thus allowing the window to return to itsinitial transparent state. Pt nanoparticles adhered to the ITO surfaceserve as an enhanced metal nucleation seed layer to allow for uniformmetal electrodeposition on a large scale without significantly affectingthe transmissivity or conductivity of the electrode. Such windowspromise the potential to switch between transparent and color-neutralopaque states in under a minute over thousands of cycles.

For any electrochromic “smart” window technology to show viability inthe market, it must be durable enough to last at least 20-30 yearswithout signs of degradation. While some academic research groups haveemployed RME for optical switching devices, these have typically beenfor reversible mirrors, small-scale pixel displays, or electronic paperapplications. In addition to durability and cost effectiveness, anyviable RME window must also be scalable to a sufficiently large size(e.g., 1 m² or more) for use in window applications, should achieveneutral color transmission characteristics across the applicable tintingspectrum, should provide fast switching speed, and the ability toprovide zero or near zero transmission, so as to provide a full blackoutprivacy state when fully tinted.

SUMMARY

The present disclosure relates to reversible metal electrodeposition(RME) for use in dynamic windows and similar devices, examples of whichinclude, but are not limited to windows, greenhouses, electric and othervehicles, transition sunglasses, goggles, tunable optics, clear-to-blackmonitors or other displays, adjustable shutters, IR modulators, thermalcamouflage, and the like. An exemplary metal-based dynamic window devicemay include a transparent or translucent conductive electrode. Thedevice further includes an electrolyte in contact with the transparentor translucent conductive electrode, the electrolyte comprising metalcations in solution that can be reversibly electrodeposited onto thetransparent or translucent conductive electrode. A counter electrode(e.g., also transparent or translucent) is also included, where theelectrolyte is sandwiched between the electrodes. The electrolytefurther comprises an additive configured to enhance the surfacemorphology of deposited metal cations during reversible metalelectrodeposition, so as to enhance one or more of color neutrality,transmittance of visible wavelengths, infrared reflectance, or switchingspeed of the dynamic window.

In an embodiment, the electrolyte additive may be a polymer, examples ofwhich include a polyol, an amine-based polymer, or a cellulosederivative. More specific examples of such additives include polyvinylalcohol, polyvinyl pyrrolidone, or hydroxyethyl cellulose.

In an embodiment, the electrolyte additive can be one or more of aninhibitor as used in electroplating, an accelerator as used inelectroplating, a leveler as used in electroplating, or an organic orinorganic molecule that similarly serves to enhance the surfacemorphology of a deposited film formed from the metal cations duringreversible metal electrodeposition onto the transparent electrode.

In an embodiment, the electrolyte additive is present in the electrolytein an amount of up to 10% by weight, at least 0.001% by weight, or from0.01% to 1% by weight.

In an embodiment, the additive reduces an RMS surface roughness of areversibly deposited metal layer onto the transparent electrode to avalue that is less than 30 nm, less than 25 nm, less than 20 nm, lessthan 15 nm, less than 10 nm, or less than 5 nm.

In an embodiment, the dynamic window is configured to achieve a nearzero transmissivity to provide a privacy state, where transmission ofvisible light wavelengths after full tinting is 1% or less, 0.1% orless, 0.01% or less, or 0.001% or less.

In an embodiment, the dynamic window is configured to achieve a highinfrared reflectance of wavelengths in the range of 700 nm to 1200 nmthat is at least 30%, at least 40%, at least 50%, at least 60%, or atleast 70%.

In an embodiment, the dynamic window is configured to achieve colorneutral characteristics with a chroma (C*) of less than 10, less than 8,or less than 5, over an operative VLT range of the dynamic window.

In an embodiment, the dynamic window is configured to achieve colorneutral characteristics with |a*| and/or |b*| values of less than 5,over an operative VLT range of the dynamic window.

In an embodiment, the metal cations in the electrolyte comprise copper(e.g., copper and bismuth).

In an embodiment, the electrolyte is an aqueous electrolyte solution.

In an embodiment, the electrolyte may be free of metal oxides, such asused in conventional metal oxide electrochromic dynamic windows.

In an embodiment, the electrolyte further comprises an anion selectedfor its ability to (i) maintain solubility of components in theelectrolyte solution and/or (ii) minimize or prevent etching of thetransparent or translucent conductive electrode. An example of such ananion is perchlorate. In an embodiment, the electrolyte solution may befree of chloride ions.

In an embodiment, the device may be operable with fast switching speedsas described herein, with relatively low applied voltages (e.g., no morethan 2V, or no more than 1V, such as 0.5 to 1V, or 0.6 to 0.8 V).

Another embodiment is directed to an electrochromic dynamic windowarticle capable of reversible metal electrodeposition, comprising atransparent or translucent conductive electrode, an electrolyte solutionin contact with the transparent or translucent conductive electrode, theelectrolyte solution comprising metal cations that can be reversiblyelectrodeposited onto the transparent or translucent conductiveelectrode upon application of a cathodic potential, and a counterelectrode, wherein the electrolyte solution further comprises anadditive that is an inhibitor, an accelerator, a leveler, or an organicor inorganic molecule that similarly serves to enhance the surfacemorphology of the metal cations during reversible metalelectrodeposition onto the transparent electrode.

Features from any of the disclosed embodiments may be used incombination with one another, without limitation. For example, any ofthe compositional or other limitations described with respect to oneembodiment may be present in any of the other described embodiments. Inaddition, other features and advantages of the present disclosure willbecome apparent to those of ordinary skill in the art throughconsideration of the following detailed description and the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A: expanded schematic view of an exemplary dynamic window.

FIG. 1B: schematic illustration of dendritic metal electrodepositionthat occurs without electrolyte additives as described herein.

FIG. 1C: schematic illustration of how adsorbed polymer inhibitorspromote smooth metal electrodeposition.

FIG. 1D: magnified view of electrode-electrolyte interface with anadsorbed polyol inhibitor or similar additive. The polymer adsorbs tothe electrode and homogenizes the flux of metal cations to the platingsurface.

FIG. 1E: scanning electron microscopy (SEM) image of metalelectrodeposits after 1 minute of deposition without electrolyteadditives.

FIG. 1F: atomic force microscopy (AFM) of electrodeposits presented inFIG. 1E.

FIG. 1G: SEM of metal electrodeposits after 1 minute of deposition with0.1 wt. % PVA dissolved in the plating solution.

FIG. 1H: AFM of electrodeposits presented in FIG. 1G. For the samplesmeasured in FIGS. 1E-1H, a voltage of −0.8 V versus Ag/AgCl was appliedto platinumized ITO working electrodes. Note the scale bar difference inFIGS. 1F and 1H.

FIGS. 2A-2E show various transmittance spectra. FIG. 2A: transmittancespectra of 5 cm×5 cm dynamic window without additive.

FIG. 2B: transmittance spectra of 5 cm×5 cm dynamic window with 0.1 wt.% PVA after four different deposition times.

FIG. 2C: transmittance at 550 nm (where the human eye is most sensitive)versus time for 120 seconds of metal deposition;

FIG. 2D: the charge density versus time required for the deposition.

FIG. 2E: coloration efficiency at 550 nm versus contrast ratiocalculated with data in FIGS. 2C-2D. A plating voltage of −0.8 V wasapplied to the dynamic window for three minutes to elicit metaldeposition.

FIG. 3A: transmittance spectra of metal-based dynamic windows for sevendistinct optical states and the switching times required to achieve eachstate.

FIG. 3B: reflectance spectra measured through the ITO-on-glass electrodewhere the metal film initially forms for the seven optical states(outdoor reflectance).

FIG. 3C: reflectance spectra measured through the metal counterelectrode that samples the top surface of the deposited metal films(indoor reflectance).

FIG. 3D: solar heat gain coefficient (SHGC) versus visible lighttransmittance (VLT) for the optical range of metal-based dynamic windows(Metal) compared to industry leaders Sage Glass (Sage) and View, Inc.(View).

FIG. 3E: chroma (C*) versus visible light transmittance (VLT) with thecondition for neutral color indicated. All optical data for the Sage andView windows in FIGS. 3A-3E were obtained from a public database (IGDBv29.0).

FIG. 4A: current density and charge density versus time for 300 secondsof electrodeposition.

FIG. 4B: sheet resistance and film thickness versus time for samplesmeasured at five distinct deposition times (15 s, 30 s, 60 s, 120 s, and300 s).

FIG. 4C: voltage drop from edge to center of a 1 ft² ITO electrode as afunction of deposition time.

FIG. 4D: transmittance at 550 nm versus time measured at three differentspots of a 1 ft² dynamic window to demonstrate uniform tinting from edgeto center.

FIG. 4E: 1 ft² dynamic window in clear state with uniformity measurementlocations indicated.

FIG. 5: cyclic voltammogram of Bi—Cu electrolyte without polymer andwith addition of 0.1 wt. % PVA measured in a 3-electrode cell with aPt-ITO working electrode, Pt wire counter electrode and Ag/AgClreference electrode at a scan rate of 20 mV/s. The shift in depositionoverpotential and decrease in current density indicate an inhibitoreffect.

FIG. 6A: cyclic voltammogram (CV) of Bi—Cu ClO₄ electrolyte with 0.1 wt.% PVA of four different molecular weights.

FIG. 6B: the corresponding transmittance curves at 550 nm measuredin-situ during the CV scan. The CV was measured in a 3-electrode cellwith a Pt-ITO working electrode, Pt wire counter electrode and Ag/AgClreference electrode at a scan rate of 20 mV/s.

FIG. 7: transmittance (at 550 nm) versus time during constant-voltagedeposition at −0.8 V versus Ag/AgCl on a Pt-ITO electrode for Bi—Cuelectrolytes with two different PVA molecular weights at a fixedconcentration. The experiment was performed in a 3-electrodespectroelectrochemical cell and transmittance was measured in-situ.

FIG. 8: transmittance (at 550 nm) versus time during constant-voltagedeposition at −0.8 V versus Ag/AgCl on a Pt-ITO electrode for Bi—Cuelectrolytes with two different PVA concentrations at a fixed molecularweight. The experiment was performed in a 3-electrodespectroelectrochemical cell and transmittance was measured in-situ.

FIG. 9: cyclic voltammogram of Bi—Cu ClO₄ electrolyte with two differentconcentrations of PVA at a fixed molecular weight. The CV was performedin a 3-electrode setup with a Pt-ITO working electrode, a Pt wirecounter electrode, and a Ag/AgCl reference electrode at a scan rate of20 mV/s.

FIGS. 10A-10B show reflectance spectra of windows with active area of 25cm² after 1 minute of tinting at a potential of −0.8 V.

FIG. 10A: reflectance spectra of the window with the control electrolyte(without any additives).

FIG. 10B: reflectance spectra of the window with 0.1 wt. % PVA. Thewindow with the PVA additive is more reflective due to the smoothermetal morphology.

FIG. 11: solar heat gain coefficient (SHGC) versus visible lighttransmittance (VLT) for the optical range of metal-based dynamic windowscompared to industry leaders Sage Glass (Sage) and View, Inc. (View).The VLT data is plotted on a logarithmic scale to distinguish theprivacy state that is unique to the present metal-based windows.

FIGS. 12A-12C: 2-dimensional projections of L*a*b* coordinates for sevendistinct optical states of dynamic windows based on reversible metalelectrodeposition. The metal-based dynamic windows exhibit trueclear-to-gray-to-black color transition across the optical range.

FIGS. 13A-13C: 2-dimensional projections of L*a*b* coordinates for fouroptical states of Sage Glass dynamic windows (from IGDB v29.0).

FIGS. 14A-14C: 2-dimensional projections of L*a*b* coordinates for fouroptical states of Sage Glass dynamic windows (from IGDB v29.0).

FIG. 15: cyclic voltammograms of Bi—Cu perchlorate electrolyte withthree different concentrations of Bi and Cu ions. The current densitydecreases with the metal ion concentration. The CV was performed in a3-electrode setup with a Pt-ITO working electrode, a Pt wire counterelectrode, and a Ag/AgCl reference electrode at a scan rate of 20 mV/s.

FIG. 16: sheet resistance versus film thickness of theoretical Cu filmassuming ideal resistivity of 1.68×10⁻⁸ ohm-m and the measured sheetresistance versus film thickness of the BiCu film electroplated onPt-ITO with the perchlorate and PVA electrolyte as described herein (seeFIG. 4B). This figure illustrates the potential to reduce the sheetresistance of the electrode as the window tints.

FIG. 17: cyclic voltammogram of Bi—Cu halide electrolyte with twodifferent concentrations of PVA. The CV was performed in a 3-electrodesetup with a Pt wire working electrode, a Pt wire counter electrode, anda Ag wire pseudo-reference electrode at a scan rate of 20 mV/s.

FIG. 18: cyclic voltammogram of Bi—Cu halide electrolyte with twodifferent concentrations of PEG. The CV was performed in a 3-electrodesetup with a Pt wire working electrode, a Pt wire counter electrode, anda Ag wire pseudo-reference electrode at a scan rate of 20 mV/s.

FIG. 19: cyclic voltammogram of Bi—Cu halide electrolyte with twodifferent concentrations of PVP. The CV was performed in a 3-electrodesetup with a Pt wire working electrode, a Pt wire counter electrode, anda Ag wire pseudo-reference electrode at a scan rate of 20 mV/s.

FIG. 20: cyclic voltammogram of Bi—Cu halide electrolyte with twodifferent concentrations of PEG with ultrahigh molecular weight(Mw=5,000,000). The CV was performed in a 3-electrode setup with a Ptwire working electrode, a Pt wire counter electrode, and a Ag wirepseudo-reference electrode at a scan rate of 20 mV/s. Current densitydecrease with concentration is attributed to an increase in solutionviscosity.

FIG. 21: viscosity of Bi—Cu halide electrolyte with varyingconcentration of hydroxyethyl cellulose (HEC) compared to commonliquids.

FIG. 22: cyclic voltammogram of Bi—Cu halide electrolyte with twodifferent concentrations of hydroxyethyl cellulose (HEC). The CV wasperformed in a 3-electrode setup with a Pt-ITO working electrode, a Ptwire counter electrode, and a Ag wire pseudo-reference electrode at ascan rate of 20 mV/s. Current density decrease with concentration isattributed to an increase in solution viscosity.

FIG. 23A: chronoamperometry at −0.4 V in Bi—Cu electrolyte with twoconcentrations of HEC using a Pt-ITO working electrode and a Agreference electrode.

FIG. 23B: transmittance (at 550 nm) versus time measured in-situ duringthe chronoamperometry experiments in FIG. 23A.

FIGS. 24A-24B show SEM images of metal electrodeposits plated on aPt-ITO electrode from a Bi—Cu halide electrolyte. FIG. 24A is with 0%HEC and FIG. 24B is with 2% HEC. In each case, deposition was at −0.4 Vfor 120 seconds with a Ag reference electrode. SEM was performed atoperating voltage of 5 kV.

FIG. 25: transmittance (at 550 nm) versus time of dynamic windowscontaining Bi—Cu halide electrolyte with different polymer additives. Adistinct dynamic window was fabricated and measured for each electrolytecomposition. Transmittance is plotted for one switching cycle consistingof plating at −0.8 V for 60 seconds followed by stripping at +0.8 V. Thedynamic window architecture is shown in FIG. 1A.

FIG. 26: transmittance (at 900 nm) versus time of dynamic windowscontaining Bi—Cu halide electrolyte with different polymer additives. Adistinct dynamic window was fabricated and measured for each electrolytecomposition. Transmittance is plotted for one switching cycle consistingof plating at −0.8 V for 60 seconds followed by stripping at +0.8 V.

FIG. 27: reflectance (at 550 nm) versus time of dynamic windowscontaining Bi—Cu halide electrolyte with different polymer additives. Adistinct dynamic window was fabricated and measured for each electrolytecomposition. Reflectance is plotted for one switching cycle consistingof plating at −0.8 V for 60 seconds followed by stripping at +0.8 V.

FIG. 28: reflectance (at 900 nm) versus time of dynamic windowscontaining Bi—Cu halide electrolyte with different polymer additives. Adistinct dynamic window was fabricated and measured for each electrolytecomposition. Reflectance is plotted for one switching cycle consistingof plating at −0.8 V for 60 seconds followed by stripping at +0.8 V.

FIGS. 29A-29C show SEM images of metal electrodeposits plated on aPt-ITO electrode from a Bi—Cu halide electrolyte. FIG. 29A shows suchwith no polymer additives, FIG. 29B shows such with 0.1 wt. % PVA, andFIG. 29C shows such with 0.1 wt. % PVP. In each case, tinting was at−0.8 V for 60 seconds with a Ag/AgCl reference electrode. SEM wasperformed at an operating voltage of 5 kV.

FIG. 30: schematic view of modeled insulating glass unit (IGU). Dynamicglass layer is 5 mm thick and oriented to face the outside of thebuilding. The clear glass layer (NSG Pilkington Optifloat™ Clear) is 6mm thick and oriented to face the inside of the building. The12.7-mm-thick gas layer consisting of 90% Ar/10% air is sandwichedbetween the glass layers to form the complete double-pane unit. Surfaces1-4 are labeled according to convention.

The drawings and figures are not necessarily drawn to scale, unlessotherwise indicated, but instead are drawn to provide a betterunderstanding of the components, and are not intended to be limiting inscope, but to provide exemplary illustrations.

DETAILED DESCRIPTION

The present disclosure relates to reversible metal electrodeposition(RME) for use in dynamic windows and similar devices, examples of whichinclude, but are not limited to windows, greenhouses, electric and othervehicles, transition sunglasses, goggles, tunable optics, clear-to-blackmonitors or other displays, adjustable shutters, IR modulators, thermalcamouflage, and the like. As shown in FIG. 1A, an exemplary metal-baseddynamic window device may typically include a transparent electrode, acounter electrode, with an electrolyte layer sandwiched therebetween.Glass layer(s) may also be present, as suggested in FIG. 1A. Theelectrolyte layer includes metal cations that are substantiallycolorless (i.e., provide substantially no tint) when in solution, butprovide tinting when a cathodic (reducing) potential is applied to thetransparent electrode (e.g., a tin oxide such as indium tin oxide(“ITO”)), resulting in deposition of metal atoms from the electrolyteonto the transparent electrode surface, resulting in a tinting of thatsurface. So long as the electrical potential is maintained, metal atomscontinue to plate on the surface, and the window progressively tints.Once a desired level of tint is achieved, the electrical potential maybe removed and the tint is maintained. When the polarity applied to theelectrodes is reversed, the deposited metal atoms are oxidized,dissolving back into the electrolyte layer, returning the window to itstransparent state. It is important that the transparent electrode isconfigured to allow stripping of the electrodeposited metal layer. Forexample, this differs from U.S. Pat. No. 9,383,619 to Kim, in which theelectrode is surface treated (e.g., with an oxygen plasma followed bysilane treatment), to interfere with the ability to strip away theelectrodeposited metal layer. In an embodiment, no such oxygen plasmaand/or silane or similar treatments of the transparent electrode(s) areperformed to increase affinity between the electrode and theelectrodeposited metal layer, in a manner that would prevent subsequentreversal (i.e., stripping).

An important aspect of the present disclosure is directed to addition ofselect additives for inclusion in the electrolyte solution layer betweenthe electrodes. Such additives serve to improve the surface morphologyof the metal layer as it grows during electrodeposition, e.g., improvingsurface smoothness, density, particle size, etc. Such additives mayenhance the resulting dynamic window's color neutrality, transmittanceof visible light wavelengths (e.g., ability to achieve a near 0%transmissivity to provide an effective “full blackout privacy state”),infrared reflectance (e.g., affecting solar heat gain), or switchingspeed. By way of example, the morphology of the deposited metal filmaffects such properties, and additives selected for inclusion in theelectrolyte layer are selected for their ability to affect suchmorphology.

Examples of such additives that may be suitable for use may be known aslevelers, inhibitors, or accelerators, as used in plating baths used inthe manufacture of microelectronic devices, where deposition of metalatoms is permanent (e.g., when forming a conductive copper tracing orthe like for a microelectronic device). Examples of such additivesinclude, but are not limited to various polymeric and other additives,examples of which include polyols (e.g., polyvinyl alcohol orpolyethylene glycol), amine-based polymers (e.g., polyvinylpyrrolidone),or cellulose derivatives (e.g., hydroxyethyl cellulose). While suchadditives may have been used to some extent in manufacture ofmicroelectronic devices, where a permanent conductive tracing or similarstructure is being deposited onto a silicon or similar semiconductivesubstrate, such additives have not been used to any significant extentin reversible metal electrodeposition electrolytes, particularly in thecontext of RME dynamic windows. A wide variety of such additives mayprove suitable for use, e.g., so long as they are stable in the presenceof other components present in the electrolyte, and they do not attackor degrade the transparent electrode or counter electrode or glasslayer(s) between which the electrolyte is sandwiched. For example, itcan be important that the selected morphology adjusting additive becompatible with any anion selected for inclusion in the electrolyte, asdescribed in Applicant's U.S. Patent Application No. 62/968,502 and PCTApplication No. PCT/US2021/015851, each of which is titled ELECTROLYTEFOR DURABLE DYNAMIC GLASS BASED ON REVERSIBLE METAL ELECTRODEPOSITION,filed Jan. 31, 2020 and Jan. 29, 2021, respectively, each of which isherein incorporated by reference in its entirety.

Polyols, amine-based polymers, cellulose derivatives, and otherexemplary suitable additives when in the electrolyte solution ascontemplated herein are colorless, preferably non-toxic, relativelyinexpensive, and electrochemically stable, so as to be compatible withreversible electrodeposition chemistry, where the metal ions in theelectrolyte may be repeatedly deposited, and stripped away, overthousands of cycles, over years of use in such a dynamic window. Therequirements for reversible electrodeposition chemistry as contemplatedherein are more stringent than for typical plating baths as used inmicroelectronics manufacture, as the system must be configured tosupport reversible metal film growth and dissolution over thousands ofcycles, with no significant degradation within the system, from onecycle to another. For example, in typical plating baths, chloride ionsare added to serve as a bridge between the metal being deposited and thepolymer or other additive, as such inhibitors are generally ineffectivewithout the inclusion of chloride ions. As described in the abovereferenced U.S. and PCT Patent Applications, such chloride ions can beundesirable in the present reversible systems, as they lead to formationof insoluble compounds, and can lead to degradation of the electrodes insuch an RME dynamic window system, after prolonged cycling. Thus, in anembodiment, the electrolytes contemplated herein are substantially voidof chloride (Cr) ions, other halide ions, or so called pseudohalide ions(e.g., cyanide ions or thiocyanate ions). Where such ions may bepresent, in an embodiment, they may be present in a molar concentrationratio relative to the metal cation that is 5:1 or less, 4:1 or less, 3:1or less, 2:1 or less, 1:1 or less, 0.5:1 or less, or 0.1:1 or less. Thevast majority (e.g., at least 60%, at least 70%, at least 80%, at least90%, or at least 95%) of the electrolyte solution may comprise water(e.g., the balance of the electrolyte solution may be water, beyond thevarious components detailed herein). As described in the abovereferenced application, in an embodiment, the electrolyte may includeperchlorate (ClO₄) ions, which do not exhibit such problems, but stillincrease the ionic conductivity of the electrolyte solution. The choiceof solvent, electrolyte, metals, and supporting ions can be importantfor building a high-performance system that achieves reversible metalfilm growth and dissolution over thousands of cycles, as therequirements for reversible electrodeposition chemistry are morestringent than for typical plating baths. For example, in the case of aPVA additive, the polyol hydroxyl groups can strongly adsorb to oxidesurfaces and thus are effective inhibitors despite the absence of Cl⁻ orother halide ions in the electrolyte solution.

As described in the previously referenced application, various metalcations may be employed for reversible electrodeposition. In anembodiment, at least one of copper (e.g., Cu²⁺) or bismuth (e.g., Bi³⁺)are employed. Numerous other metals (e.g., transition metals in theperiodic table) may also be suitable for use. Copper and bismuth exhibitsimilar standard reduction potentials (i.e., +0.337 V and +0.308 V,respectively). When used together, copper and bismuth exhibit synergyduring electrodeposition that improves the reversibility of the system.By way of example, where two such metals are employed, their standardreduction potentials may be within 25%, within 20%, within 15%, orwithin 10% of one another. It will be apparent that other metal cationsmay also be suitable for use as the plating cation(s). The metal cationcomponent (e.g., Cu(ClO₄)2, BiOClO₄ or the like) may be included inconcentration of at least 0.1 mM, 1 mM, or 5 mM, up to 10M, up to 5M, orup to 1M, such as from 1 mM to 100 mM, or 1 mM to 50 mM.

By way of example, the electrolyte solution may also contain a componentconfigured to increase ionic conductivity. LiClO₄ is an example of such.By way of non-limiting example, an exemplary electrolyte may include 10mM Cu(ClO₄)2, 10 mM BiOClO_(4, 10) mM HCl₄, 1M LiClO₄, and a smallamount of one or more of the additives described herein, in water (e.g.,deionized water). In an embodiment, the morphology adjusting additivemay be included in an amount of at least 0.001%, such as from 0.01% to10%, or from 0.1% to 1% by weight of the electrolyte solution.

A polymer additive may be of any suitable molecular weight, e.g., of upto 10 million Daltons, up to 5 million Daltons, or up to 1 millionDaltons, such as greater than 1,000 Daltons, from 5,000 Daltons to 1million Daltons, from 10,000 Daltons to 1 million Daltons, from 30,000Daltons to 500,000 Daltons, from 30,000 Daltons to 250,000 Daltons, orfrom 40,000 Daltons to 100,000 Daltons. Molecular weight values may bereported as number average or weight average molecular weights. By wayof further non-limiting example, an exemplary polymeric additive (e.g.,PVA or otherwise) may have a weight average molecular weight of 61,000Daltons. Relatively lower molecular weight additives will typicallyexhibit greater solubility, and may result in lower viscosity for theelectrolyte solution.

Inclusion of the additive may decrease the surface roughness of thedeposited metal film layer, resulting in a deposited layer that is lessporous (e.g., less formation of dendrites), smoother, more dense, ofmore uniform morphology, with generally smaller particles (e.g.,generally spherical), where the particles exhibit a relatively narrowsize distribution, as compared to a similar electrolyte, but without theadditive.

FIGS. 1B-1D schematically illustrate deposition mechanisms for thepresent systems. While there remains some debate over the mechanism bywhich polymer inhibitors work, most studies agree that the effect on themetal morphology stems from adsorption of the additive molecules on theelectrode surface. In this mechanism, the polymers form an adsorbedmonolayer on the electrode that aids in achieving uniform plating.According to the prevailing Chazalviel space charge model, when metalelectrodeposition is diffusion-limited (as is the case for the dilutemetal concentrations used for dynamic windows) the concentration of ionsdrops to zero near the electrode surface and the localized electricfields that form at inhomogeneities cause ramified growth or what isloosely termed dendritic electrodeposition (FIG. 1B). With the adsorbedpolymer layer, however, the space charge remains distributed rather thanlocalized over the surface and electrodeposition occurs uniformlythrough competition for adsorption sites between the metal cations andpolymer side groups (FIG. 1C). The polymer gains positive charge fromthe metal ions in solution that coordinate with the polymer, and thischarged layer polarizes the electrode and homogenizes the ion flux. FIG.1D shows a magnified view of the electrode-electrolyte interface with anadsorbed polymer additive as described herein (e.g., a polyolinhibitor). The polymer adsorbs to the electrode and homogenizes theflux of metal cations to the plating surface.

When the electrolyte does not include such an additive, the metaltinting or opacifying layer that is reversibly deposited onto theinterior surface of the transparent electrode tends to be formed fromrelatively tall, narrow metal pillars with a wide size distribution, andlow surface coverage (i.e., discontinuities included therein), as shownin SEM images and AFM measurements (e.g., see FIGS. 1E-1F). With theaddition of a small amount of an additive as contemplated herein (e.g.,0.1% by weight of PVA), the resulting reversible deposition metal layeris far smoother (e.g., RMS surface roughness of less than 30, less than25, less than 20, less than 15, less than 10, or even less than 5 nm).In addition to such improved smoothness, the surface also exhibits anoverall more uniform morphology (e.g., see FIGS. 1G-1H).

When including such an additive, the polymer layer formed from theadditive polarizes the electrode, and introduces an additional energybarrier to nucleation (i.e., an increase in overpotential). Such resultsin a decrease in deposition rate (but with increased overall smoothness,and more uniform surface morphology) as the metal ions must diffusethrough the charged polymer additive layer and compete with the polymerfor adsorption sites on the electrode surface.

As described herein, molecular weight and/or concentration of thepolymer or other additive can be varied within a fairly wide range,while still providing effective control over resulting surfacemorphology. While a wide range of molecular weights may prove suitablefor use as an additive as contemplated herein, in an embodiment, it maybe advantageous for the additive to have a molecular weight of no morethan 250,000 Daltons, or no more than 100,000 Daltons, as such lowermolecular weight additives may be more easily dissolved, and may resultin relatively lower viscosities for the electrolyte solution.

The additive may be included in an amount of at least 0.001%, (1000 ppm)such as from 0.01% to 10%, or other ranges as disclosed herein. Evenlower concentrations may prove suitable for use, such as at least 10ppm, or at least 100 ppm, as such levels may still be sufficient to meeta threshold critical limit for surface coverage of the transparentelectrode where electrodeposition occurs. The electrolyte may berelatively insensitive to additive concentration, so long as thethreshold critical limit for surface coverage is met. By way of example,for a polyol, the critical limit may be estimated by calculating thenumber of hydroxyl groups in solution provided by such a polyoladditive, compared to the number of adsorption sites on the electrodesurface. For a 0.1% polymer additive concentration, the number ofhydroxyl groups in solution may far exceed the number of adsorptionsites, e.g., by about 5 orders of magnitude. As such, it will beapparent that relatively small concentrations of the additive may besufficient to achieve the desired inhibitor result. It will be apparentthat concentrations far lower than 0.1% may be suitable for use (e.g.,such as 0.01%, 0.001%, or even lower values, of 100 ppm, or less, solong as sufficient additive is provided for surface coverage to achievethe desired inhibition). While described in the context of a polyolinhibitor, it will be appreciated that analogous considerations mayapply for an accelerator additive, or a leveler additive. A wide varietyof additives and concentrations thereof may be suitable for use so longas the selected additive(s) are capable of enhancing the surfacemorphology (e.g., increased density (i.e., reduced porosity) to thedeposited metal layer, increased smoothness, increased uniformity inparticle sizes, etc.), so as to provide good color neutrality, near 0%transmission of visible light wavelengths associated with a fullblackout privacy state, high infrared reflectance, and/or fast switchingspeed for the dynamic window incorporating such an electrolyte.

In an embodiment, a polyol additive (e.g., such as PVA) may beadvantageous, as it may exhibit improved compatibility with aperchlorate or other selected anion, as compared to various nitrogencontaining additives (such as PVP), or cellulose derivative additives(such as HEC). While PVA is an example of a particularly suitableadditive, it will be appreciated that other polymers, or evennon-polymer small molecule additives may also be suitable, where suchother additives exhibit a similar ability to control morphology of metalgrowth during reversible metal electrodeposition.

Additives known in electroplating as inhibitors may act to create andmaintain a stable diffusion layer that promotes smooth and denseelectrodeposition. Such additives may also sometimes be referred to assuppressors in the electroplating art. Non-limiting examples of suchadditives include various polyols (e.g., PVA, PEG, PAG, and the like),amine-based polymers (PVP, PEI, and the like), and cellulose derivatives(HEC, MPC, EC, and the like). Those of skill in the art will appreciatethat numerous other examples are also possible.

Additives known in electroplating as accelerators may typically besulfur-containing compounds. Accelerator additives serve to block highpotential sites (i.e. defects), forcing the metal ions to plateelsewhere. Such additives may also sometimes be referred to asbrighteners in the semiconductor art. Non-limiting examples of suchadditives may include organic sulfides, disulfides, thioethers,thiocarbamates, as well as other sulfur-containing compounds capable ofblocking defect sites to metal deposition. Specific examples ofaccelerator additives include, but are not limited to bis-(sodiumsulfopropyl)-disulfide (“SPS”).

Additives known in electroplating as levelers may typically bequaternary nitrogen compounds. Leveler additives serve to block highpotential sites (i.e. defects), in a similar manner as accelerators,yielding smoother electrodeposited films. Non-limiting examples of suchadditives may include but are not limited to quaternary nitrogencompounds (e.g., ammonium salts) such as cetyltrimethylammonium bromide,Janus Green B, and triethyl-benzyl-ammonium chloride. It will beappreciated that more than one additive, including combinations ofdifferent types of additives, may be employed.

Various other organic or inorganic molecules capable of providingsimilar adjustment to the morphology of the electrodeposited metal layermay also be useful as suitable additives. An example of such may besodium citrate. Others will be apparent to those of skill in the art, inlight of the present disclosure.

FIGS. 2A-2B illustrate how inclusion of an additive as contemplatedherein can improve the speed at which tinting occurs (e.g.,transmittance through the window drops faster), and can increase themaximum degree of tinting finally achievable within a reasonable timeframe (e.g., 20 minutes, 10 minutes, 5 minutes, 3 minutes, or evenfaster, such as 1 minute or less). By way of example, as shown in FIG.2B, transmittance of visible light wavelengths once fully tinted (after3 minutes in this example) can be near 0% (e.g., 1% or less, 0.1% orless, 0.01% or less, or 0.001% or less). Because the additive serves toinhibit plating as described, it is surprising that the addition of theadditive can actually speed up tinting.

Inclusion of such an additive can also improve the efficiency of theresulting window, e.g., reducing the rate of charge consumption for thewindow, where such an additive is included in the electrolyte solution.FIGS. 2D-2E illustrate such an effect. The lower charge consumption andincreased switching speed gives the resulting window a colorationefficiency (defined as change in optical density over a fixed area perunit charge) that is significantly higher (e.g., 2-3× higher) than acomparable window, where the electrolyte does not include such anadditive.

As shown in FIG. 10A, in addition to improved switching speed, a fullblackout privacy state (near 0% transmission when tinted), and improvedefficiency, inclusion of the additive also can improve heat rejection ofthe resulting window. For example, when such an additive is not present,the porous, discontinuous film allows light to be transmitted throughthe gaps between metal deposits. The morphologically “spiky” particlesseen in FIG. 1F also result in increased scattering and absorption forthe resulting film. Such scattering and absorption results in poor heatrejection, as infrared wavelengths in particular are absorbed. Theadditive slows down plating rate, but improves switching speed, as theresulting film is smoother, denser, and more uniform, better able toreflect incident infrared wavelengths that would result interior heating(which may be undesired in at least some circumstances). Furthermore,the additives allow tuning between reflective (good heat rejection) andabsorptive (good heat retention) states, as in some cases it may bedesirable to absorb heat rather than reflect it (e.g., in cold winterweather climates).

In addition to performance parameters noted above, visible lighttransmittance (“VLT”), solar heat gain coefficient (“SHGC”), and chroma(to what degree the window is “color neutral” as it tints) are alsoimportant performance characteristics, which can be improved where theelectrolyte includes an additive as contemplated herein. The presentmetal-based dynamic windows can provide VLT, SHGC and chromacharacteristics that are equal to or better than that provided byexisting technologies. FIGS. 3A-3C show transmittance (“T”) andreflectance (“R”) across the wavelength range of 300 to 2500 nm (e.g.,generally corresponding to the relevant bandwidth for solar radiation).Such figures show transmittance and reflectance for various opticalstates for a dynamic window, from its “clear” state to a “privacy”state, through progressively tinted optical states.

Transmittance in the clear state is generally dictated by transmittancethrough the ITO or other transparent electrode, and the aqueouselectrolyte, along with the two outer layers of glass or other glazingmaterial (e.g., plastic, such as plexiglass). The overall shape of thetransmittance curve is maintained as the window tints because theelectroplated metal film blocks light generally uniformly across thesolar spectrum. The full blackout privacy state with near 0%transmittance is a distinct advantage of the present embodiments overcommercially available competing technologies, which do not provide suchlow, near 0% transmittance (i.e., effectively providing blackoutcurtains in the dynamic window). As noted above, this near 0%transmittance is facilitated by inclusion of an appropriate additive inthe electrolyte, which allows the metal to deposit as a dense, ratherthan porous layer.

The reflectance in the clear state is primarily dictated by the ITO orother transparent electrode that serves as a low-emissivity coating thattransmits visible light, while reflecting infrared wavelengths (e.g.,λ>700 nm, such as 700 nm to 2500 nm, or 700 nm to 1200 nm). Reflectanceof the dynamic window increases across the solar spectrum as the windowtints, because the metal film becomes more reflective as it grows,particularly on the exterior face of the window. The exhibited highinfrared reflectance (e.g., at least 30%, at least 40%, at least 50%, atleast 60%, or at least 70%) of wavelengths in the range of 700 to 1200nm is particularly important for energy control, as about half of allincident solar energy is in this regime. As noted above, where it may bedesirable to absorb heat rather than reflect it, the additive and otherelectrolyte solution constituents can be selected and particularlyconfigured to achieve such.

In addition, FIGS. 3B-3C show how the reflectance properties of thedynamic windows may differ with viewing direction (i.e., from inside tooutside of the window, vs. from outside to inside the window). Generallyspeaking, the surface where the metal nucleates (e.g., the ITOelectrode) is more reflective, while the opposite top surface may bemore absorptive, providing a “matte” appearance. In an embodiment, thereflective surface can be oriented towards the exterior of the building,where it can more efficiently reject light and heat, while theabsorptive “matte” surface may be oriented inwardly for a more desirableaesthetic.

Returning to VLT and SHGC, VLT refers to the fraction of light in thevisible spectrum (e.g., from about 400 to 700 nm) that passes throughthe window, while SHGC refers to the percentage of solar radiation thatenters a building through the window. A higher SHGC is generallydesirable in cold climates, while a low SHGC is desired in hot climates.Traditional static windows employ a spectrally-selective stack of metalfilms and anti-reflection layers to maximize transmittance of visiblelight wavelengths, while reflecting infrared wavelengths. However, suchstatic windows do not provide any way to adjust to an outdoorenvironment that is in flux. FIG. 3D shows SHGC and VLT characteristicsfor state of the art dynamic windows available from Sage Glass and View,Inc. FIG. 3D also plots the SHGC and VLT characteristics for examples ofthe presently contemplated metal-based dynamic windows, which arecapable of operating over a wider range of SHGC and VLT combinations.Such dynamic windows allow a user to adjust the optical properties (SHGCand/or VLT) according to the local climate, or seasonal conditions. Itis a further advantage that such changes to the optical properties ofthe dynamic window are achievable with relatively modest powerconsumption, to alter the thickness of the reversibly deposited metallayer.

Color associated with windows is another important consideration. Onedrawback of existing dynamic window technologies is that such windowsare not particularly color neutral, but appear somewhat yellow whenclear, and exhibit a blue color shade as they tint. Chroma (C*) is ameasure of color in the CIE L*a*b* color space, often used to evaluatecolor or chromatic characteristics. When C* is <10, the human eye hasdifficulty distinguishing the color of the object, and it is perceivedas a neutral gray. As shown in FIG. 3E, the present metal-based dynamicwindows are able to achieve C* of less than 10, less than 8, or evenless than 5, over the entire operative VLT range. As shown in FIG. 3E,state of the art dynamic windows do not provide such color neutraloperation. Of course, the neutral color characteristics of the presentwindows may be referenced to a* and/or b*, where C* is equal to thesquare root of the sum of (a*)²+(b*)². For example, in an embodiment,the dynamic window may achieve color neutral characteristics with theabsolute value of a* and/or b* of less than 5, over an operative VLTrange of the dynamic window.

Another advantage of the present use of the contemplated additives iswith respect to minimizing voltage drop across a large (e.g., 1 m² ormore) dynamic window transparent electrode, so as to achievesubstantially uniform tinting across the window. Existing dynamicwindows reduce switching speed, lowering current density requirements,to achieve more uniform tinting over such large windows. By way ofexample, such windows often take about 20 minutes to transition acrosstheir full optical range. It is an advantage to be able to provide afull available tinting transition within a faster time period, e.g.,with 15 minutes, within 10 minutes, within 5 minutes, within 3 minutes,within 2 minutes, within 1 minute, within 30 seconds, or within 15seconds. For example, use of additives as described herein may allowswitching from a clear window to a full blackout privacy state within aslittle as 15 seconds.

Dynamic windows based on RME enable a unique strategy for reducingresistance of the electrode, as metals are generally excellentelectrical conductors, and deposition of a continuous film across theelectrode decreases the resistance of the electrode as the film growsthicker, if the film is substantially continuous. This approach is notpossible with earlier generation RME windows, because the metalelectrodeposits were not particularly continuous, but relativelyisolated and discontinuous or porous, as shown in FIGS. 1E-1F. As shownin FIGS. 1G-1H, with the inclusion of the additive as contemplatedherein, the deposited film is far more continuous and less porous,resulting in increased electrode conductivity as the window tints. FIGS.4A-4E plot such properties of current density, charge density, sheetresistance, voltage drop, and shows the relatively uniform transmittancethat results from the presently contemplated dynamic windows. Suchwindows also show increased durability (e.g., >1000 cycles) of a copperor other conductive mesh counter electrode embedded in such a dynamicwindow, where the electrolyte includes a small amount of additive (e.g.,PVA). For example, FIGS. 4G-4H of the provisional Application, alreadyincorporated by reference, show photographs comparing the durability ofsuch a copper mesh counter electrode both with, and without theadditive.

In an embodiment, the counter electrode is a nonpolymeric electrode,such as a metallic electrode. For example, in an embodiment, the counterelectrode may be a highly conductive material, rather than comprising arelatively poorly conducting polymeric conductive material (e.g.,polyaniline, polypyrrole, polythiophene or derivatives or mixturesthereof). In addition to exhibiting lower conductivity, such polymericcounter electrodes are typically not color neutral, interfering with theability to achieve excellent color neutrality as described herein.

EXAMPLES AND EXPERIMENTAL RESULTS Methods

Chemicals were received from commercial sources and used without furtherpurification. Electrochemical studies were carried out using a SP-150Biologic potentiostat. For experiments utilizing three electrodes,electrochemical potentials were measured and reported in reference to a“no-leak” Ag/AgCl (3 M KCl) reference electrode (eDAQ). ITO-on-glasstransparent electrodes with a sheet resistance of 10 Ω/sq (XinyanTechnology Ltd.) were cleaned by ultrasonication in de-ionized H₂O with10% Extran solution for 10 min, acetone for 5 min, and isopropanol for10 min, sequentially. Next, the electrodes were dried under a stream ofN₂ or air and then placed in a UVO-cleaner (Jelight Company Inc, ModelNo 42) for 10 min to remove organic contaminants. To form the Pt-ITOelectrodes, an aqueous dispersion of 1000 ppm Pt nanoparticles with 3 nmaverage diameter (Sigma-Aldrich) was diluted 10:1 with deionized waterand then spray deposited with a 20 mm 113 kHz Ultrasonic Mist Atomizer(WHDTS) onto the ITO-on-glass electrodes. Then, the electrodes wereannealed in air at 250° C. for 20 minutes before use. The sub-monolayerof 3-nm-diameter Pt nanoparticles for promoting uniform nucleation ofthe metal electrodeposits does not affect the optical or electricalproperties of the ITO in any significant way. The ITO electrode used ismerely exemplary, and it will be appreciated that other transparentelectrodes could additionally or alternatively be used.

The immersed geometric surface area of the working electrode was 1.0 cm²for the three-electrode experiments. Spectroelectrochemical measurementswere performed in a 4.5 cm by 2.0 cm by 1.0 cm glass cuvette (G205,Labomed, Inc.) in a three-electrode configuration with Pt-modifiedITO-on-glass as the working electrode, a Pt wire counter electrode, anda “no-leak” Ag/AgCl (3 M KCl) reference electrode (eDAQ). Theperchlorate electrolyte comprised 10 mM Cu(ClO₄)₂, 10 mM BiOClO₄, 10 mMHClO₄, and 1 M LiClO₄ dissolved in deionized water. The halide-basedelectrolyte comprised 15 mM CuCl₂, 5 mM BiCl₃, 10 mM HCl, and 1 M LiBrdissolved in deionized water. The various polymer additives testedincluded polyvinyl(alcohol), polyethylene glycol, polyvinyl pyrrolidone,and hydroxyethyl cellulose. All the polymers were purchased fromSigma-Aldrich as powders, and polymers with variable molecular weightwere obtained for the relevant experiments. All polymers were dissolvedin the control electrolyte by placing a vial of electrolyte with animmersed PTFE stir bar on a hot plate set to 60° C. and 1200 RPM for 1hour. The concentration of polymer in solution varied from 0.1 wt. % to10 wt. % and was a variable of study.

Small-scale dynamic windows used for the optical performancecharacterization were constructed with 5 cm×5 cm Pt-modified ITO onglass and a Cu foil frame around the edge (see FIG. 1A for schematic).The electrolyte for the small-scale windows was the control electrolytewith 0.1 wt. % PVA (Mw=61,000). Butyl rubber Solargain edge tape with athickness of 2 mm and a width of 5 mm (Quanex Inc.) served as the frameof the dynamic windows. Conductive nylon tape (ElectricMosaic, Z22)enabled electrical contact to the perimeter of the ITO electrode. Thetotal window thickness was 5 mm.

Large-scale dynamic windows comprised the same layers with the exceptionof a Cu mesh electrode used in place of the Cu foil frame. The windowswere constructed with 30 cm×30 cm Pt-modified ITO-on-glass or 5 cm×15 cmPt-modified ITO on glass and transparent Cu mesh (TWP, Inc., wirediameter: 0.0012 in) as the electrodes. The electrolyte for theprototypes had the same components as the control electrolyte with theconcentration of the Cu(ClO₄) and the BiOCl₄ diluted to 5 mM. Butylrubber Solargain edge tape with a thickness of 2 mm and a width of 5 mm(Quanex Inc.) served as the frame of the dynamic windows. Conductivenylon tape (ElectricMosaic, Z22) enabled electrical contact to theperimeter of the ITO electrode.

In-situ optical measurements (transmittance and reflectance) weremeasured with an Ocean Optics FX spectrometer coupled with an OceanOptics halogen light source (HL-2000-FHSA) and a reflectance probe.Applicant did not have the capability to perform in-situ transmittancemeasurements of 1 ft² devices but were able to perform the opticalmeasurements on 6-inch dynamic windows with the electrode contact at oneedge to simulate the behavior of a 1 ft² window. Complete optical dataused for the performance modeling was collected from 300-2500 nm with 2nm increments using a Cary 5000 UV-VIS-NIR spectrometer coupled with aUniversal Measurement Accessory (Cary, UMA). SEM was performed witheither a FEI NovaLab 600i scanning electron microscope operated at anaccelerating voltage of 5 kV or an FEI Magellan 400 XHR scanningelectron microscope operated at an accelerating voltage of 5 kV. Surfacetopology was measured with a NanoSurf easyScan 2 atomic forcemicroscope.

Optical performance modeling was conducted using Window 7.7 (LBNL) andOptics 6 (LBNL) software. Glazing data for the View, Inc. and SageGlasswindows was obtained from the International Glazing Database (IGDBv29.0). Specifically, the Optics 6 software was used to analyze andconvert the raw spectrophotometry measurements for the metal-baseddynamic windows, and the WINDOW 7 software was used to model the IGUwith the various glazing layers and degrees of tint. The WINDOW 7software includes algorithms for calculating VLT and SHGC that areconsistent with the standards set by ASHRAE SPC 142, IS015099, and theNational Fenestration Rating Council (NFRC). The dimensions of the IGUwere selected to model a typical unit and the thickness and orientationof each layer is shown schematically in FIG. 30. The dynamic glass layeris 5 mm thick and faces outside of the building and the clear glasslayer is 6 mm thick and serves as the inward-facing portion of the IGU.There is a 12.7 mm gas layer consisting of 90% argon/10% air in betweenthe glass layers. The NSG Pilkington Optifloat™ Clear glass product wasselected as the clear glass layer because it has high visible and solartransmittance and neutral color.

Results

FIGS. 1E-1H present SEM and AFM measurements for metals deposited at−0.8 V vs. Ag/AgCl for one minute on platinized ITO (Pt-ITO) electrodeswith and without a 0.1 wt. % addition of PVA (Mw: 61,000) to theelectrolyte. The control film grown without any additives (i.e. 0% PVA)is rough (RMS: 46.2 nm) and was comprised of metal pillars with a widesize distribution and low surface coverage (see FIGS. 1E-1F). This filmmorphology is typical of metal growth in a dilute concentration case.The plating solution with 0.1 wt. % addition of PVA, in contrast,deposits a smooth (RMS: 4.05 nm), uniform morphology (see FIGS. 1G-1H).The metal film is compact and comprised of generally spherical particleswith a relatively narrow size distribution.

The efficacy of inhibitors in plating solutions is often characterizedelectrochemically. It is common to observe electrode polarization anddecreased current density (i.e. plating rate) when a polymeric layerforms on the electrode surface. This effect is readily observed byperforming cyclic voltammetry (CV) experiments in a three-electrode celland relating the current-voltage relationship between a control solutionand a solution with the polymer additive. FIG. 5 shows CV data for thecontrol electrolyte and the electrolyte with 0.1 wt. % PVA. The solutionwith PVA exhibits an increase in the deposition overpotential (80 mVshift) and lower current density as a function of voltage compared tothe control solution. Both the shift in overpotential and reducedcurrent density are indicative of the inhibitor effect in theelectroplating solution. The polymer layer polarizes the electrode andintroduces an additional energy barrier to nucleation (i.e. increase inoverpotential). The deposition rate is reduced because the metal ionsmust diffuse through the charged polymer layer and compete with thepolymer for adsorption sites on the electrode surface.

Molecular weight and concentration of the polymer can be importantvariables that can affect the thickness and density of the polymercoating as well as the viscosity of the solution. To illustrate such,spectroelectrochemical data for electrolytes with variable molecularweight and concentration of PVA were gathered to understand thesignificance of these variables in the present systems. No cleardependence of the electrochemical response or optical change wasobserved in the molecular weight range of 31,000 to 205,000 g/mole (seeFIGS. 6A-7). It was also observed that the concentration of polymer inthe electrolyte does not affect the electrochemical kinetics or filmoptics (see FIG. 8-9). The absence of trends for molecular weight andpolymer concentration is in agreement with the proposed adsorption-basedinhibition mechanism. For PVA, there is one hydroxyl group (i.e.adsorption site) per monomer unit and the molecular weight determinesthe number of repeat units per polymer chain. At a fixed weightpercentage, the total number of monomer units (with one hydroxyl groupper unit) in solution is the same regardless of the molecular weight. Inthe adsorption mechanism, the inhibitor works as long as there issufficient concentration of polymer to form a complete monolayer andthus the molecular weight of the polymers is not a significant factor aslong as this criterion is met. That said, as described herein, molecularweight can affect the viscosity and dissolution characteristics, and somay be selected based on such desired criteria.

This same understanding explains the insensitivity to polymerconcentration provided the concentrations studied exceed the criticallimit for surface coverage. Through a simple calculation, one cancompare the quantity of hydroxyl groups in solution at some knownpolymer concentration to the number of adsorption sites on the electrodesurface. For 0.1 wt. % polymer concentration, the number of hydroxylgroups in solution exceeds the number of adsorption sites by about fiveorders of magnitude. It is clear that the concentration of polymer inthe tested electrolyte far exceeds the requirement for forming acomplete monolayer on the electrode surface.

The detailed calculation is presented below.

Adsorption Sites Calculation

Molecular weight of monomer unit of PVA:

M = 44.07  g/mol

Concentration of PVA in Electrolyte

C = 0.1  wt.  % = 1  g/L (assuming  density  of  water)

Number Concentration of Hydroxyl Groups in Electrolyte

$\left( \frac{1\mspace{14mu}{mol}}{44.07\mspace{14mu} g} \right)\left( \frac{1\mspace{14mu} g}{L} \right)*{\left. N_{A} \right.\sim 10^{22}}\mspace{14mu} L^{- 1}$

Projected 2D Area of Water Molecule

${\pi r}^{2} = {{{\pi\left( {1.375\mspace{14mu}{nm}} \right)}^{2} \approx {6\mspace{14mu}{{nm}^{2}\left( \frac{1\mspace{14mu}{cm}^{2}}{10^{14}\mspace{14mu}{nm}^{2}} \right)}}} = {6*10^{- 14}\mspace{14mu}{cm}^{2}}}$

Number of Water Molecule “Sites” Per Cm² of Electrode Area

$\left( \frac{1}{6*10^{- 14}\mspace{14mu}{cm}^{2}} \right) \approx {1.7*10^{13}\mspace{14mu}{{cm}^{- 2}\left( {{simplifying}\mspace{14mu}{adsorption}\mspace{14mu}{sites}\mspace{14mu}{to}\mspace{14mu}{squares}\mspace{14mu}{instead}\mspace{14mu}{of}\mspace{14mu}{circles}} \right)}}$

Volume of Electrolyte Per Cm² of Device Area

(1  cm)(1  cm)(0.5  cm) = 0.5  cm³(assuming  electrolyte  layer  is  5  mm  thick)

Compare Volumetric Concentration of Sites in Solution (Hydroxyl Groups)and Areal Concentration of Sites on the Electrode Surface (AdsorptionSites) Hydroxyl Sites in Solution Per Cm² of Device Area

${\left( {10^{22}\mspace{14mu}{sites}\mspace{14mu} L^{- 1}} \right)\left( \frac{1\mspace{14mu} L}{1000\mspace{14mu}{cm}^{3}} \right)\left( {0.5\mspace{14mu}{cm}^{3}} \right)} = {5*10^{18}\mspace{14mu}{sites}}$

Adsorption Sites on Surface Per Cm2 of Device Area

1.7 * 10¹³  cm⁻² ∼ 10¹³  sites 5 * 10¹⁸  sites>> 10¹³  sites

We chose to add 0.1 wt. % PVA (Mw: 61,000) to the electrolyte forsubsequent experiments because it was the lowest concentration thatcould be reproducibly added to small-volume batches of solution.Further, the polymer molecular weight did affect the process time forpreparing solutions (higher molecular weight PVA took longer to dissolvein the electrolyte) so it was advantageous to work with the lowermolecular weight polymers. At commercial scale, the relative toleranceof the inhibitor to concentration and molecular weight may easemanufacturability because variance in the polydispersity and weightpercentage of the polymer additive should have little to no effect onthe window performance.

We did not restrict our study to PVA and experimented with otherwater-soluble polymers like polyethylene glycol (PEG), polyvinylpyrrolidone (PVP), and hydroxyethyl cellulose (HEC). Of the polymerstested, however, PVA was the most viable candidate, as it did notproduce solubility issues in the perchlorate-based electrolyte used inthis work. While the experiments conducted may primarily focus onPVA-electrolytes as the model case, it is important to note that thereare numerous polymers and small molecules that can exhibit morphologycontrol for reversible metal electrodeposition, that could alternativelyor additionally be used.

Exploring Other Polymers

In addition to PVA, we experimented with other water-soluble polymerslike polyethylene glycol (PEG), polyvinyl pyrrolidone (PVP), andhydroxyethyl cellulose (HEC). PEG is a polyol that is similar to PVA butcontains oxygen atoms in the polymer backbone instead of the side group.PVP is not a polyol and has an amide unit in the side group, as do manyother electroplating additives. HEC is a cellulose derivative used as athickening agent in aqueous products like shampoo. The molecularstructure of each polymer is shown below.

Of the polymers tested, PVA is the only candidate that did not producesolubility issues in the perchlorate-based electrolyte used in thiswork. This electrolyte is optimized for long-term durability butexhibits higher sensitivity to additives. We did not, however, observeany solubility issues with these additives in the halide-basedelectrolyte used in our previous work, which permitted further study ofthe different polymers. The Bi—Cu halide-based electrolyte was asdescribed in the Methods section above.

PVA, PEG, and PVP exhibited an inhibitor effect in the Bi—Cu halidesystem. Cyclic voltammograms (CVs) measured in the Bi—Cu halideelectrolyte for each polymer are shown in FIGS. 17-19. For each of thethree polymers we observed the above referenced increase inoverpotential and decrease in current density. Similar to the PVAresults discussed, no trend was observed for changes in concentration.Similarly, no trend was observed for changes in molecular weight for thepolymers tested in FIGS. 17-19. However, when testing a PEG additivewith ultrahigh molecular weight (Mw=5,000,000) a trend for concentrationwas observed, wherein higher polymer concentration led to decreasedcurrent density (see FIG. 20). Such is believed to be due to increasedsolution viscosity. A similar observation was made with the HECadditive. FIG. 21 plots solution viscosity for varying concentrations ofHEC. FIG. 22 shows a similar decrease in current density with increasingpolymer concentration measured with CV. HEC did not cause an increase indeposition overpotential, but did yield increased switching speed atshort times (see FIGS. 23A-23B). SEM shows that the HEC promoted adenser film morphology (which explains the initial switching speedincrease seen in FIG. 24A-24B), but the metal film remains discontinuousand thus has the same transmittance as the control at longer depositiontimes (see FIG. 25). Thus, increased viscosity from HEC plays a role inhow the metal films form even if the polymer is not strongly adsorbed tothe surface. It is, however, a weaker effect as compared to the resultswith the PVA inhibitor. Returning to the PVA example, after confirmingthat PVA promoted a measurable effect on the metal film morphology, weprobed the optical response that arises from the structure of thedifferent films.

Superior Optical Performance

Metal films comprised of particles often appear quite different fromtheir bulk, mirror-like counterparts. When familiar reflectors like goldand silver are broken down into nanoparticles and embedded into glass,the brilliant colors of stained glass emerge and bear no indication oftheir metallic origin. The shape, size, and environment of metalparticles on the nanoscale serve as the design parameters for creatingmetal films with the desired macroscale effect. For dynamic windows, thereflective properties of metals are attractive for controlling solarheat gain, but too much reflection can have aesthetic, and even legal,consequences. According to one embodiment, the right balance is a ‘blackmirror’ appearance that absorbs a significant fraction of visible lightand reflects most of the infrared spectrum (i.e. heat) when the windowis tinted.

To measure the optical properties of the different metal morphologies, 5cm×5 cm dynamic windows were fabricated with and without the polymerinhibitor in solution, and in-situ transmittance measurements wereperformed during three minutes of tinting (i.e. metal deposition) at apotential of −0.8 V. The transmittance spectra at four different timepoints are plotted for the control device (without additives) in FIG. 2Aand for the dynamic window with 0.1 wt. % PVA in the electrolyte in FIG.2B. A schematic view of the dynamic window architecture is presented inFIG. 1A and photographs of the devices are included in the provisionalapplication. The transmittance at 550 nm (where the human eye is mostsensitive) versus switching time is plotted for both devices in FIG. 2C.By comparing the optical response of the control device (withoutadditives) and the dynamic window that contains 0.1 wt. % addition ofPVA in the electrolyte, it is clear that the polymer inhibitor elicitsimproved switching speed, color neutrality (i.e. substantially flatresponse across the visible spectrum), and contrast (down to 0.001%transmittance for privacy).

The polymer inhibitor also makes the dynamic windows more efficient.Coloration efficiency is an important metric for assessing dynamicwindows that use electrochemical reactions and is defined as the changein optical density over a fixed area per unit charge. Dynamic windowswith higher coloration efficiency require less energy to switch andyield less voltage drop across practical-scale electrodes. FIG. 2D plotscharge density versus time and shows that the rate of charge consumptionis lower for the dynamic window with the PVA inhibitor. The combinationof the lower rate of charge consumption and the increased switchingspeed (see FIGS. 2C-2D) gives the dynamic window with the polymerinhibitor a coloration efficiency that is 2-3× higher than the controldevice depending on the desired contrast (see FIG. 2E).

The improvement in optical performance and efficiency is attributed tothe metal film morphology that forms in the presence of the PVAadditive. Without any additives in solution, the metal film isdiscontinuous and light can transmit through the pores or gaps betweenmetal deposits. The ‘spiky’ particles also increase scattering (and thusabsorption) events and yield a film that is absorptive, and thus poor atrejecting heat (see FIG. 10A). The polymer inhibitor slows down theplating rate and supports deposition of smooth, uniform metal deposits.The resulting metal films are dense and efficient at blocking light andyield windows that reflect, rather than absorb, heat (see FIG. 10B). Theuse of polymer inhibitors for controlling the electrodeposit morphologyis important for striking the right balance between power consumptionand optical modulation in dynamic windows.

The optical performance of dynamic windows with a PVA additive in theelectrolyte was investigated by measuring the transmittance (T) andreflectance (R) in the 300<λ<2500 nm wavelength range corresponding tosolar radiation over the series of optical states accessible to thetechnology. T(λ) and R(λ) are plotted in FIGS. 3A-3C for seven distinctoptical states of dynamic windows with the PVA inhibitor additive. Theshape of the transmittance spectrum in the clear state is determined bythe transmittance through the ITO and aqueous electrolyte along with thetwo outer layers of glass. This shape is maintained as the window tintsbecause the electroplated metal film blocks light uniformly across thesolar spectrum. An important advantage of metal-based dynamic windowsover competing technologies is an exclusive “full blackout privacystate” with, e.g., 0.001% visible transmittance that functions likeblackout curtains for providing quality sleep (see FIG. 3A). Such aprivacy state is made possible by the dense metal morphology facilitatedby the PVA or other additive. The reflectance spectrum in the clearstate is primarily dictated by the ITO that serves as a low-emissivitycoating that transmits visible light and reflects infrared wavelengths(λ>700 nm, or >1200 nm, such as 700 nm to 2500 nm, or 700 nm to 1200nm). The reflectance increases across the solar spectrum as the windowtints because the metal film becomes more reflective as it grows. Thehigh infrared reflectance (700<λ<2500 nm) of up to 70% in someembodiments is important for energy control as about half of solarenergy is in this regime. Additionally, the reflectance properties ofthe dynamic windows can differ with the viewing direction (see FIG. 3Bvs. FIG. 3C). The reflectance spectra in FIG. 3B were measured throughthe side of the device with the ITO electrode, and the spectra in FIG.3C were measured through the side of the device with the metal counterelectrode (see FIG. 1A for a schematic view of the device layers). Thesurface where the metal nucleates (i.e. the ITO electrode) is morereflective while the top surface of the metal (shown in FIGS. 1G-1H) ismore absorptive and has a matte appearance. Further, light that reflectsoff the top surface of the metal must travel back through theelectrolyte where it can be scattered or absorbed. Thus, in anembodiment the reflective surface can be oriented towards the exteriorof the building where it can efficiently reject light and heat. Theabsorptive side exhibiting a “matte” appearance can face inward where amirror-like appearance may be aesthetically undesirable to the peopleindoors.

As already noted, the principal optical metrics for windows are visiblelight transmittance (VLT) and solar heat gain coefficient (SHGC). Thevisible light transmittance is the fraction of light in the visiblespectrum (˜400<λ<˜700 nm) that passes through the window. A high VLTprovides daylighting that can offset electric lighting, but also causesglare under direct sun. The solar heat gain coefficient is thepercentage of solar radiation that enters a building through the window.This includes incident radiation that is directly transmitted throughthe window and absorbed radiation that is subsequently re-radiated intothe building. A high SHGC is desirable in cold climates to offsetheating loads, and a low SHGC is important in hot climates to managecooling loads. Static windows use a spectrally-selective stack of metalfilms and anti-reflection layers with specific thicknesses thattransmits visible light and reflects the infrared. The problem withstatic windows, however, is that the outdoor environment is in flux. Forexample, a static window configured to reflect infrared wavelengths maybe desirable in the summer months or in a hot climate, but the oppositewould be desirable in the winter months or in a cold climate.

Dynamic windows that access a range of VLT|SHGC combinations introduce anew paradigm. With dynamic windows, users can adjust the opticalproperties according to the local climate without sacrificing theprimary function of their window: the view. In the present dynamicwindows, with a modest voltage, the thickness of the metallic layer isadjusted to strike the right balance of daylighting and solar gainthroughout each day. The best static windows use metal films to findthis balance. The advance of dynamic metal films with tunable thicknesscould propel a new generation of windows that adapt to the user'spreferences and environment.

To compare the optical performance of RME windows to other dynamicwindow technologies, a double-pane insulating glass unit (IGU) wasmodeled and the performance metrics were calculated. A description andjustification of the modelling parameters and calculations is providedin the “IGU Modeling” section below.

IGU Modeling

Definitions:

Visible Light Transmittance (VLT): the fraction of visible light (380 nmto 720 nm), weighted by sensitivity of the human eye, that transmitsthrough the window. It is a dimensionless value from 0 to 1.

${VLT} = {\int\limits_{380\mspace{14mu}{nm}}^{720\mspace{14mu}{nm}}{{T(\lambda)}{E(\lambda)}}}$

Here T(λ) is the spectral transmittance at a given wavelength innanometers and E(λ) is the incident solar spectral irradiance. Whenintegrated over the visible portion of the electromagnetic spectrum, theequation yields the total fraction of transmitted visible light.

Solar Heat Gain Coefficient (SHGC): the fraction of incident solarradiation admitted through a window, both directly transmitted andabsorbed and subsequently release inward. SHGC is calculated from 300 nmto 2500 nm (i.e. solar spectrum). It is a dimensionless value from 0 to1.

${SHGC} = {\int\limits_{300\mspace{14mu}{nm}}^{2500\mspace{14mu}{nm}}{{T(\lambda)}{E(\lambda)}}}$

Here T(λ) is the spectral transmittance at a given wavelength innanometers and E(λ) is the incident solar spectral irradiance. Whenintegrated over the solar radiation spectrum, the equation yields thetotal fraction of transmitted solar energy.

Color (Chroma and L*a*b*)

The universal system for quantifying color is the CIE L*a*b* color spacethat is designed to model human color perception with three coordinates.L* is a luminance coordinate from dark (black) to light (white), a* is acoordinate between red and green, and b* is a coordinate between yellowand blue. Each (L*,a*,b*) point specifies a color and the axes arelinear with respect to the sensitivity of the human eye. Assessing colorneutrality is simplified by introducing a fourth coordinate called the“chroma” (C*) where:

$C^{*} = \sqrt{a^{*2} + b^{*2}}$

When C*<10, the human eye has difficulty distinguishing the color of theobject and it is perceived as gray (neutral).

Modeling Methodology

To model the dynamic window technologies as a full insulating glass unit(IGU), the Windows and Daylighting software suite was used, which isavailable through the Lawrence Berkeley National Laboratory (LBNL). TheOptics 6 software was used to analyze and convert the rawspectrophotometry measurements for the metal-based dynamic windows, andthe WINDOW 7 software was used to model the IGU with the various glazinglayers and degrees of tint. The WINDOW 7 software includes algorithmsfor calculating VLT and SHGC that are consistent with the standards setby ASHRAE SPC 142, ISO15099, and the National Fenestration RatingCouncil (NFRC).

The dimensions of the IGU were selected to model a typical unit and thethickness and orientation of each layer is shown schematically in FIG.30. The dynamic glass layer is 5 mm thick and faces outside of thebuilding and the clear glass layer is 6 mm thick and serves as theinward-facing portion of the IGU. There is a 12.7 mm gas layerconsisting of 90% Argon/10% Air in between the glass layers. Theemissivity of the glass on surfaces 1, 3, and 4 is assumed to be 0.84and the emissivity of the low-emissivity coating on surface 2 is assumedto be 0.15. The NSG Pilkington Optifloat™ Clear glass product wasselected as the clear glass layer because it has high visible and solartransmittance and neutral color. This enables a fair comparison betweenthe different electrochromic technologies.

The optical data for the metal-based dynamic windows was obtained bymeasuring the transmittance and reflectance (through both orientations)from 300 nm to 2500 nm for seven distinct optical states. This data ispresented in FIGS. 3A-3C. The data was formatted according to theInternational Glazing Database (IGDB) standard and imported into theglazing database in the WINDOW 7 software program.

The optical data for the View, Inc. and SageGlass products were publiclyavailable in IGDB v29.0 and imported into the WINDOW 7 software program.Each technology had optical data available for four different tintstates that was used for further calculations.

The visible light transmittance, the solar heat gain coefficient, andthe color coordinates (L*a*b*) for each optical state of each technologywere calculated. There were seven optical states for the metal-baseddynamic windows, four states for the SageGlass windows, and four statesfor the View, Inc. windows. All of the calculated data is presentedbelow in Table 1.

TABLE 1 Product - Tint State VLT SHGC L* a* b* Chroma* SageGlass - Clear0.622 0.473 83.43 −4.69 15.3 16.00 SageGlass - 20% T 0.210 0.167 53.18−12.2 −0.49 12.21 SageGlass - 6% T 0.059 0.107 29.66 −10.4 −7.52 12.83SageGlass - 1% T 0.016 0.089 13.49 −6.49 −7.81 10.15 View, Inc. - Tint 10.561 0.465 79.22 −3.66 19.52 19.86 View, Inc. - Tint 2 0.397 0.29568.87 −5.01 16.57 17.31 View, Inc. - Tint 3 0.201 0.165 51.69 −6.39 9.5611.50 View, Inc. - Tint 4 0.030 0.094 20.31 −8.40 −4.16 9.37 Metal -Clear 0.760 0.603 89.93 −2.81 −1.02 2.99 Metal - Tint 1 (5 s) 0.6050.526 82.1 −2.64 1.42 3.00 Metal - Tint 2 (15 s) 0.385 0.341 68.34 −1.762.57 3.11 Metal - Tint 3 (30 s) 0.282 0.267 60.02 −0.98 2.96 3.12Metal - Tint 4 (60 s) 0.145 0.160 44.84 −0.33 3.7 3.71 Metal - Tint 5(120 s) 0.079 0.108 33.68 0.08 4.32 4.32 Metal - Privacy (180 s) 0.000010.045 0.03 0.01 0.00 0.01

The calculated values of visible light transmittance (VLT), solar heatgain coefficient (SHGC), color coordinates (L*a*b*), and chroma shown inTable 1 were calculated using the WINDOW 7 software (for the Sage andView products), and calculated by modeling the IGU shown schematicallyin FIG. 30 for those of the present disclosure (Metal).

FIG. 3D presents the VLT|SHGC space for the present metal-based dynamicwindows (“Metal”) and two commercially available dynamic window productsfrom industry leaders View, Inc. and SageGlass. FIG. 11 plots the VLTdata from FIG. 3D on a logarithmic scale to emphasize the privacy statethat is unique to the present windows that use metal electrodeposition.

The “Metal” IGU boasts the largest dynamic range of the technologieswith ΔT_(vis)=0.76 and ΔSHGC=0.56. The metal-based dynamic windowsachieve a higher ΔT_(vis) than the competing technologies because thedesign does not require relatively thick (>1 μm) oxide electrodes thatabsorb visible light. The dynamic windows achieve a superior ΔSHGCbecause of the high clear-state transmittance and reflective (versusabsorptive) properties of the metal film (see FIGS. 3B-3C).

As noted above, the color of windows is an equally importantconsideration. Most people prefer a neutral color transition(clear-to-gray-to-black) that does not distort the appearance of theirindoor environment. Indeed, color is often cited as one of the largestdrawbacks of existing technology that often appears yellow when clearand turns blue as it tints. As noted, where Chroma (C*) is <10 (orabsolute value of a* and/or b* is <5), the human eye has difficultydistinguishing the color of the object and it is perceived as gray(neutral). FIG. 3D, plots the C* vs. VLT for the three evaluated windowtechnologies. The dynamic windows that use metal as the active layerexhibit neutral color over their entire optical range. FIGS. 12A-14C,plot projections of the L*a*b* coordinates for the optical states ofeach technology, illustrating the undesirable yellow and blue colortints of the competing technologies, as compared to the desired gray ofthe present disclosure.

1 Ft² Dynamic Windows

A major challenge for deploying electrochromic technologies at scale isminimizing voltage drop across the transparent electrode and achievinguniform tinting across the window. All materials (sans superconductors)possess internal resistance to current flow that scales with thedistance the charge must traverse. For windows, this problem isexacerbated by the requirement for transparent conductors that aregenerally 100× more resistive than common conductors like copper.Applicant developed an analytical model of electrode resistance forelectrochromic windows and derived a simple equation for the voltagedrop across a square electrode, as shown in equation 1 below. Thevoltage drop often yields non-uniform tinting.

$\begin{matrix}{{{{\Delta V} = \frac{{JR}_{sh}L^{2}}{8}};}{{J = {{current}\mspace{14mu}{density}}},{R_{sh} = {{sheet}\mspace{14mu}{resistance}}},{L = {{electrode}\mspace{14mu}{length}}}}} & \left( {{eq}.\mspace{14mu} 1} \right)\end{matrix}$

There are several strategies for achieving uniform tinting overlarge-area (>1 m²) windows. The most common approach is to slow down theswitching speed and thus lower the current density required for thewindow to tint. As a result, the majority of commercial electrochromicwindows take ˜20 minutes to transition across their optical range.Kinestral Technologies has pioneered the use of patterned electrodesthat enable their HALIO® product to tint “10× faster” than incumbenttechnologies, but this perk comes at a cost premium. A final strategy toachieve fast and uniform tinting is to decrease the sheet resistance ofthe electrodes. However, none of the efforts to reduce the electroderesistance have been successful at a large scale.

Dynamic windows based on reversible metal electrodeposition (RME) enablea unique strategy for reducing the resistance of the electrodes. Metalsare excellent conductors and deposition of continuous metal filmsdecreases the resistance of the electrodes as the metal film growsthicker. This approach was not possible in previous generations of RMEwindows, because the metal electrodeposits were isolated anddiscontinuous (see FIGS. 1E-1F). With the inclusion of an additive asdescribed herein (e.g., a PVA inhibitor), the metal film has anuninterrupted morphology as shown in FIGS. 1G-1H that yields increasedelectrode conductivity as the window tints.

FIGS. 4A-4D characterize the electrical properties of the metal film asit grows on the Pt-ITO transparent electrode. FIG. 4A plots the currentdensity and charge density versus time for 300 seconds ofelectrodeposition at −0.8 V and FIG. 4B shows the decrease in electrodesheet resistance as the metal film grows thicker over time. Thecorresponding voltage drop across a 1 ft² ITO electrode was calculatedusing Eq. 1 and plotted in FIG. 4C using the current density (J) in FIG.4A and the sheet resistance (R_(sh)) in FIG. 4B across five differentdeposition times (15 s, 30 s, 60 s, 120 s, and 300 s). Electrodepositionrate is voltage-independent over some voltage range dependent on theelectrolyte chemistry because the metal growth is diffusion-limited. Thevoltage tolerance (i.e. the voltage range where the electroplating rateis uniform) is 0.6 V for the electrolyte used in these working examples.The condition for uniform tinting in this system is highlighted in FIG.4C with a dashed line. The decrease in voltage drop over time plotted inFIG. 4C indicates that uniform tinting is possible in a 1 ft² dynamicwindow after ˜30 s of electrodeposition. To validate this hypothesis, a1 ft² dynamic window was constructed and the transmittance (at 550 nm)versus time was measured at three different spots from the center of thewindow to the edge (see FIG. 4D). As expected, the window tinted fasterat the edge (where the voltage is applied) for the first 30 seconds.However, with further electrodeposition, the optical modulation in thecenter caught up to the edge and the visible response of the entirewindow was substantially uniform. The optical response of the windowsmeasured in FIGS. 4A-4D is slower than the dynamic windows measured inFIGS. 3A-3E because the active ion concentration was reduced from 10 mMto 5 mM to lower the current density (see FIG. 15). Diluting the ionconcentration was not a viable option in previous working exampleiterations because the metal morphology became more porous upondilution. The PVA inhibitor or other additive as described herein solvesthis problem by promoting a compact morphology, irrespective of ionconcentration in the electrolyte.

The uniform deposition in a 1 ft² dynamic window is the culmination ofthree advantages of the PVA or similar additive: 2× improvement incoloration efficiency, 2× ion concentration dilution to halve thecurrent density, and the 30% reduction in sheet resistance from thecontinuous metal film. The 2× improvement in coloration efficiency meansthat 1/2 the current is needed to switch the window at a fixed speed. Byhalving the metal ion concentration from 10 mM to 5 mM, the windowoperates at half the current density, and thus half the voltage dropacross the electrode. The 30% reduction in sheet resistance lowers thevoltage drop by an additional 30%. The combination of these threefactors yields a tolerable voltage drop (<0.6 V) for uniform tinting ina 1 ft² dynamic window based on reversible metal electrodeposition. Allthese advantageous are facilitated, because of the inclusion of anelectrolyte additive as described herein.

The maximum transmittance of the 1 ft² dynamic window is ˜10% lower thanthe IGU modeled in FIGS. 3A-3E (65% versus 76%) because the large-scaleprototype used a copper mesh counter electrode instead of a metal frameelectrode shown in the device schematic in FIG. 1A, to maintain uniformion diffusion across the electrolyte layer of the device. The coppermesh comprises 30-micron-wide wires spaced 224 microns apart in a squarepattern and this mesh reflects a portion of the incident light. Inprevious working examples, the cycle life of devices was limited by thedurability of the copper mesh counter electrode, which would fail(disintegrate) after about 300 cycles. The PVA inhibitor drasticallyimproves the durability of the copper mesh by promoting uniform platingon the mesh and limiting the stripping reactions that dissolve the mesh.The mesh electrode in the device that contains 0.1% PVA showed no signsof degradation after 1000 cycles, while the mesh electrode in the devicethat included no additive as described herein showed noticeable severedisintegration of the mesh well before 1000 cycles. During such testing,each cycle comprised −0.8 V deposition for 1 minute followed by +1 Vstripping for 1 minute. The transmittance of the dynamic windows in theclear state can be increased by using a mesh with thinner wires.

Although the working examples are principally described in the contextof a PVA inhibitor as the electrolyte additive, it will be appreciatedthat a wide variety of other additives that can similarly improve theuniformity of the metal deposition morphology can additionally oralternatively be used, and are within the scope of the presentdisclosure.

Conclusion

While described principally in the context of windows, it will beappreciated that the present embodiments can be employed more broadly,e.g., in glass or plastic surfaces where dynamic tinting of the surfacemay be desired. Exemplary implementations include, but are not limitedto windows, greenhouses, electric and other vehicles, transitionsunglasses, goggles, tunable optics, clear-to-black monitors or otherdisplays, adjustable shutters, IR modulators, thermal camouflage, andthe like.

All publications, patents and patent applications cited herein, whethersupra or infra, are hereby incorporated by reference in their entiretyto the same extent as if each individual publication, patent or patentapplication was specifically and individually indicated to beincorporated by reference.

Unless otherwise stated, all percentages, ratios, parts, and amountsused and described herein are by weight.

Unless otherwise indicated, numbers expressing quantities, constituents,distances, or other measurements used in the specification and claimsare to be understood as optionally being modified by the term “about” orits synonyms. When the terms “about,” “approximately,” “substantially,”“generally” or the like are used in conjunction with a stated amount,value, or condition, it may be taken to mean an amount, value orcondition that deviates by less than 20%, less than 10%, less than 5%,less than 1%, less than 0.1%, or less than 0.01% of the stated amount,value, or condition.

Some ranges may be disclosed herein. Additional ranges may be definedbetween any values disclosed herein as being exemplary of a particularparameter. All such ranges are contemplated and within the scope of thepresent disclosure.

The phrase ‘free of’ or similar phrases if used herein means that thecomposition or article comprises 0% of the stated component, that is,the component has not been intentionally added. However, it will beappreciated that such components may incidentally form thereafter, undersome circumstances, or such component may be incidentally present, e.g.,as an incidental contaminant.

The phrase ‘substantially free of’ or similar phrases as used hereinmeans that the composition or article preferably comprises 0% of thestated component, although it will be appreciated that very smallconcentrations may possibly be present, e.g., through incidentalformation, contamination, or even by intentional addition. Suchcomponents may be present, if at all, in amounts of less than 1%, lessthan 0.5%, less than 0.25%, less than 0.1%, less than 0.05%, less than0.01%, less than 0.005%, less than 0.001%, or less than 0.0001%. In someembodiments, the compositions or articles described herein may be freeor substantially free from any specific components not mentioned withinthis specification.

In reference to various standardized tests (e.g., ISO15099 or othertests), it will be understood that reference to any such standard refersto the latest update (if any) of such standard, unless otherwiseindicated. Any such referenced standards are incorporated herein byreference, in their entirety.

The present disclosure can be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. Thus, thedescribed implementations are to be considered in all respects only asillustrative and not restrictive. The scope of the invention is,therefore, indicated by the appended claims rather than by the foregoingdescription. All changes that come within the meaning and range ofequivalency of the claims are to be embraced within their scope.

1. An electrochromic dynamic window article capable of reversible metalelectrodeposition, comprising: a transparent or translucent conductiveelectrode; an electrolyte in contact with the transparent or translucentconductive electrode, the electrolyte comprising metal cations that canbe reversibly electrodeposited onto the transparent or translucentconductive electrode; and a counter electrode; wherein the electrolytecomprises an additive configured to enhance a surface morphology ofdeposited metal cations during reversible metal electrodeposition, so asto enhance one or more of color neutrality, transmittance of visiblewavelengths, infrared reflectance, or switching speed of the dynamicwindow.
 2. The article as recited in claim 1, wherein the electrolyteadditive is a polymer.
 3. The article as recited in claim 2, wherein theelectrolyte polymer additive comprises at least one of a polyol, anamine-based polymer, or a cellulose derivative.
 4. The article asrecited in claim 3, wherein the electrolyte polymer additive comprisesat least one of polyvinyl alcohol, polyvinyl pyrrolidone, orhydroxyethyl cellulose.
 5. The article as recited in claim 1, whereinthe electrolyte additive comprises a polyol.
 6. The article as recitedin claim 1, wherein the electrolyte additive comprises polyvinylalcohol.
 7. The article as recited in claim 1, wherein the electrolyteadditive is present in the electrolyte in an amount of up to 10% byweight.
 8. The article as recited in claim 1, wherein the electrolyteadditive is present in the electrolyte in an amount from 0.01% to 1% byweight.
 9. The article as recited in claim 1, wherein the electrolyteadditive comprises an inhibitor as used in electroplating, anaccelerator as used in electroplating, a leveler as used inelectroplating, or an organic or inorganic molecule that similarlyserves to enhance the surface morphology of a deposited film formed fromthe metal cations during reversible metal electrodeposition onto thetransparent electrode.
 10. The article as recited in claim 1, whereinthe additive reduces an RMS surface roughness of a reversibly depositedmetal layer onto the transparent electrode to a value that is less than30 nm, less than 25 nm, less than 20 nm, less than 15 nm, less than 10nm, or less than 5 nm.
 11. The article as recited in claim 1, whereinthe dynamic window is configured to achieve a near zero transmissivityto provide a privacy state, where transmission of visible lightwavelengths after full tinting is 1% or less, 0.1% or less, 0.01% orless, or 0.001% or less.
 12. The article as recited in claim 1, whereinthe dynamic window is configured to achieve a high infrared reflectanceof wavelengths in a range of 700 nm to 1200 nm that is at least 30%, atleast 40%, at least 50%, at least 60%, or at least 70%.
 13. The articleas recited in claim 1, wherein the dynamic window is configured toachieve color neutral characteristics with a chroma (C*) of less than10, less than 8, or less than 5, over an operative VLT range of thedynamic window.
 14. The article as recited in claim 1, wherein thedynamic window is configured to achieve color neutral characteristicswith |a*| or |b*| values of less than 5, over an operative VLT range ofthe dynamic window.
 15. The article as recited in claim 1, wherein themetal cations comprise copper.
 16. The article as recited in claim 1,wherein the electrolyte is an aqueous electrolyte solution.
 17. Thearticle as recited in claim 1, wherein the electrolyte further comprisesan anion selected for its ability to (i) maintain solubility ofcomponents in the electrolyte and/or (ii) minimize or prevent etching ofthe transparent or translucent conductive electrode.
 18. The article asrecited in claim 17, wherein the anion comprises perchlorate.
 19. Anelectrochromic dynamic window article capable of reversible metalelectrodeposition, comprising: a transparent or translucent conductiveelectrode; an electrolyte solution in contact with the transparent ortranslucent conductive electrode, the electrolyte solution comprisingmetal cations that can be reversibly electrodeposited onto thetransparent or translucent conductive electrode upon application of acathodic potential; and a counter electrode; wherein the electrolytesolution further comprises an additive that is an inhibitor, anaccelerator, a leveler, or an organic or inorganic molecule thatsimilarly serves to enhance a surface morphology of the metal cationsduring reversible metal electrodeposition onto the transparentelectrode.
 20. The article as recited in claim 19, wherein theelectrolyte additive comprises at least one of a polyol, an amine-basedpolymer, or a cellulose derivative.
 21. The article as recited in claim19, wherein the additive reduces an RMS surface roughness of areversibly deposited metal layer onto the transparent electrode to avalue that is less than 30 nm, less than 25 nm, less than 20 nm, lessthan 15 nm, less than 10 nm, or less than 5 nm.
 22. The article asrecited in claim 19, wherein the dynamic window is configured to achievea near zero transmissivity to provide a privacy state, wheretransmission of visible light wavelengths after full tinting is 1% orless, 0.1% or less, 0.01% or less, or 0.001% or less.
 23. The article asrecited in claim 19, wherein the dynamic window is configured to achievea high infrared reflectance of wavelengths in a range of 700 nm to 1200nm that is at least 30%, at least 40%, at least 50%, at least 60%, or atleast 70%.
 24. The article as recited in claim 19, wherein the dynamicwindow is configured to achieve color neutral characteristics with achroma (C*) of less than 10, less than 8, or less than 5, over anoperative VLT range of the dynamic window.